Aflatoxin Production by Aspergillus flavus as Related to Various Temperatures

Two aflatoxin-producing isolates of Aspergillus flavus were grown for 5 days on Wort media at 2, 7, 13, 18, 24, 29, 35, 41, 46, and 52 C. Maximal production of aflatoxins occurred at 24 C. Maximal growth of A. flavus isolates occurred at 29 and 35 C. The ratio of the production of aflatoxin B₁ to aflatoxin G₁ varied with temperature. Aflatoxin production was not related to growth rate of A. flavus; one isolate at 41 C, at almost maximal growth of A. flavus, produced no aflatoxins. At 5 days, no aflatoxins were produced at temperatures lower than 18 C or higher than 35 C. Color of CHCl₃ extracts appeared to be directly correlated with aflatoxin concentrations. A. flavus isolates grown at 2, 7, and 41 C for 12 weeks produced no aflatoxins. At 13 C, both isolates produced aflatoxins in 3 weeks, and one isolate produced increasing amounts with time. The second isolate produced increasing amounts through 6 weeks, but at 12 weeks smaller amounts of aflatoxins were recovered than at 6 weeks.     

Ion Effects on Calcium Accumulation by Cardiac Sarcoplasmic Reticulum

The effects of monovalent cations on the active calcium-accumulating ability of cardiac sarcoplasmic reticulum were assessed. Grana prepared in an ion-free system accumulated calcium when ATP and Mg⁺⁺ were present. Sodium ion and to a lesser extent lithium but not K⁺ reduced the amount of calcium taken up. The reduction of calcium binding by Na⁺ is not due to inhibition of uptake but to a rapid release of the radiocalcium bound. The amount of calcium released by sodium does not appear to be enough to explain contraction on the basis of sodium influx into muscle, but may be significant in the regulation of tension.     

Application ofVerticillium lecanii for the control ofAphis gossypii by a low-volume electrostatic rotary atomiser and a high-volume hydraulic sprayer

Verticillium lecanii (Fungi: Deuteromycete) blastospores were applied to a chrysanthemum crop by an ULV electrostatically charged rotary atomiser (APE-80). The deposition of spores and subsequent control ofAphis gossypii were compared to high volume hydraulic application. A full rate treatment (2×10¹³ blastospores per ha.) was applied by the APE-80 at week 1 and reduced spore rates of 1/6^th and 1/12^th applied by both the APE-80 and the hydraulic sprayer once and twice a week respectively for weeks 1 to 6. Untreated plots served as controls. Initial deposits of spores were higher with the electrostatic sprayer and better distributed with respect to the position of the target aphids. Significantly lower aphid populations were recorded on the electrostatically treated plots in week 4. The single full rate treatment had significantly fewer aphids than the untreated plots from week 3 and all treatments had significantly fewer aphids than the untreated plots from week 5 onwards. The proportion of the aphid population killed byV. lecanii was higher on the electrostatically treated plots until week 6.      

Regulation of lipoprotein lipase in muscle and adipose tissue during exercise.

Lipoprotein lipase (LPL) is regulated in a tissue-specific manner; exercise increases LPL activity in muscle at the same time it is reduced in adipose tissue. The purpose of this study was to determine the relationship between LPL activity and LPL mRNA in muscle and adipose tissue in rats exposed to one bout of exercise. Immediately after a 2-h swim, LPL activity [pmol free fatty acids (FFA).min-1.mg tissue-1] in the exercised animals was reduced 43% in adipose tissue (110 +/- 26 to 63 +/- 17) and increased almost twofold in the soleus muscle (203 +/- 26 to 383 +/- 59) compared with sedentary control animals. At the same time, LPL mRNA was reduced 42% in adipose tissue and increased 50 and 100% in the red vastus and white vastus muscles, respectively. Twenty-four hours after the swim, LPL activity had returned to control levels in adipose tissue and the soleus muscle. At hour 24 of recovery, LPL mRNA was still reduced 23% in the adipose tissue of exercised animals but was not significantly different between exercised and control animals in any of the muscle tissues analyzed. Changes in total RNA concentration could not account for the changes in relative LPL mRNA expression. The relationship between LPL enzyme activity and LPL mRNA in muscle and adipose tissue was +0.86 and +0.93 at 0 and 24 h postexercise, respectively. Thus the tissue-specific changes in enzyme activity induced by exercise could be mediated, in part, through pretranslational control.     

Volume-activated chloride permeability can mediate cell volume regulation in a mathematical model of a tight epithelium

Cell volume regulation during anisotonic challenge is investigated in a mathematical model of a tight epithelium. The epithelium is represented as compliant cellular and paracellular compartments bounded by mucosal and serosal bathing media. Model variables include the concentrations of Na, K, and Cl, hydrostatic pressure, and electrical potential, and the mass conservation equations have been formulated for both steady-state and time-dependent problems. Ionic conductance is represented by the Goldman constant field equation (Civan, M.M., and R.J. Bookman. 1982. Journal of Membrane Biology. 65:63-80). A basolateral cotransporter of Na, K, and Cl with 1:1:2 stoichiometry (Geck, P., and E. Heinz. 1980. Annals of the New York Academy of Sciences. 341:57-62.) and volume-activated basolateral ion permeabilities are incorporated in the model. MacRobbie and Ussing (1961. Acta Physiologica Scandinavica. 53:348-365.) reported that the cells of frog skin exhibit osmotic swelling followed by a volume regulatory decrease (VRD) when the serosal bath is diluted to half the initial osmolality. Similar regulation is achieved in the model epithelium when both a basolateral cotransporter and a volume-activated Cl permeation path are included. The observed transepithelial potential changes could only be simulated by allowing volume activation of the basolateral K permeation path. The fractional VRD, or shrinkage as percent of initial swelling, is examined as a function of the hypotonic challenge. The fractional VRD increases with increasing osmotic challenge, but eventually declines under the most severe circumstances. This analysis demonstrates that the VRD response depends on the presence of adequate intracellular chloride stores and the volume sensitivity of the chloride channel.     

Cell-specific fatty acylation of proteins in cultured cells of neuronal and glial origin

Distinct sets of cellular proteins were labeled with [³H]myristic and [³H]palmitic acids in primary (rat neurons and astroglia) and continuous (murine N1E-115 neuroblastoma and rat C6 glioma) cell cultures derived from the nervous system. Both soluble and membrane proteins were modified by myristate in a hydroxylamine-stable (amide) linkage, while palmitoylated proteins were esterlinked and almost exclusively membrane bound. Chain elongation of both labeled fatty acids prior to acylation was observed, but no protein amide-liked [³H]myristate originating from [³H]palmitate was detected. Fatty acylation profiles differed considerably among most of the cell lines, except for rat astroglial and glioma cells in which myristoylated proteins appeared to be almost identical based on SDS gel electrophoresis. An unidentified 47 kDa myristoylated protein was labeled to a significantly greater extent in astroglial than in glioma cells; the expression of this protein could be related to transformation or development in cells of glial origin.     

Quantification of cytochrome P450 reductase gene expression in human tissues.

We have isolated and sequenced cDNA clones that code for a variant of human cytochrome P450 reductase. An RNase protection assay was used to quantify the corresponding mRNA in adult and fetal tissues. The results demonstrate that, in the samples analyzed, the cytochrome P450 reductase gene displays very little inter-individual variation in its expression in adult liver and is subject to little developmental or tissue-specific regulation.     

Glucocorticoids do not affect the induction of a novel calcium-dependent nitric oxide synthase in rabbit chondrocytes.

Incubation of rabbit articular chondrocytes with interleukin-1 beta caused time-dependent expression of NO synthase, determined as nitrite, after a lag period of 6h. The synthesis of nitrite was concentration-dependent and was inhibited by cycloheximide and NG-monomethyl-L-arginine, but not by dexamethasone or hydrocortisone. The synthesis of NO in the 100,000g supernatant of activated chondrocytes was inhibited by EGTA, but not by the calmodulin inhibitors W-13 or trifluoperazine. The synthesis of NO was half-maximal at approximately 20nM free Ca2+. Endotoxin also induced the expression of this NO synthase. Thus, rabbit articular chondrocytes express a novel inducible NO synthase which is Ca(2+)-dependent, and whose induction is not prevented by glucocorticoids.